Citation and License

Arthritis Research & Therapy 2011, 13:R8
doi:10.1186/ar3229

Published: 28 January 2011

Abstract

Introduction

Recent evidence suggests that intervertebral disc (IVD) cells derived from degenerative
tissue are unable to respond to physiologically relevant mechanical stimuli in the
'normal' anabolic manner, but instead respond by increasing matrix catabolism. Understanding
the nature of the biological processes which allow disc cells to sense and respond
to mechanical stimuli (a process termed 'mechanotransduction') is important to ascertain
whether these signalling pathways differ with disease. The aim here was to investigate
the involvement of interleukin (IL)-1 and IL-4 in the response of annulus fibrosus
(AF) cells derived from nondegenerative and degenerative tissue to cyclic tensile
strain to determine whether cytokine involvement differed with IVD degeneration.

Methods

AF cells were isolated from nondegenerative and degenerative human IVDs, expanded
in monolayers and cyclically strained in the presence or absence of the cytokine inhibitors
IL-1 receptor antagonist (IL-1Ra) or IL-4 receptor antibody (IL-4RAb) with 10% strain
at 1.0 Hz for 20 minutes using a Flexcell strain device. Total RNA was extracted from
the cells at time points of baseline control and 1 or 24 hours poststimulation. Quantitative
real-time polymerase chain reaction was used to analyse the gene expression of matrix
proteins (aggrecan and type I collagen) and enzymes (matrix metalloproteinase 3 (MMP3) and a disintegrin and metalloproteinase with a thrombospondin type 1 motif 4 (ADAMTS4)).

Results

Expression of catabolic genes (MMP3 and ADAMTS4) decreased in AF cells derived from nondegenerative tissue in response to 1.0-Hz
stimulation, and this decrease in gene expression was inhibited or increased following
pretreatment of cells with IL-1Ra or IL-4RAb respectively. Treatment of AF cells derived
from degenerative tissue with an identical stimulus (1.0-Hz) resulted in reduced anabolic
gene expression (aggrecan and type I collagen), with IL-1Ra or IL-4RAb pretreatment
having no effect.

Conclusions

Both IL-1 and IL-4 are involved in the response of AF cells derived from nondegenerative
tissue to 1.0-Hz cyclic tensile strain. Interestingly, the altered response observed
at 1.0-Hz in AF cells from degenerative tissue appears to be independent of either
cytokine, suggesting an alternative mechanotransduction pathway in operation.